School of Optometry, University of California, Berkeley, Berkeley, California

A. J. Jackson

Department of Ophthalmology and Optometry, Royal Victoria Hospital, Belfast, United Kingdom

H. Minto

Sight Savers International, Islamabad, Pakistan

Footnotes

Commercial RelationshipsI.L. Bailey, The University's Technology Licensing Office is applying for copyright for the visual acuity test. Any proceeds will be used to support low vision research at U.C.Berkeley, P; A.J. Jackson, None; H. Minto, None.

Purpose: :
The AMA Guides for the Evaluation of Permanent Impairment forVision was promulgated in 2001 and has been followed by theWHO and ICO. It develops Functional Acuity Scores and FunctionalField Scores by weighting both acuity and field scores (on 100-pointscales) from monocular and binocular testing. Field and acuityscores are combined by multiplication to give a Functional VisionScore(FVS). We are developing methodologies to obtain a FunctionalVision Score using methods that are easily applicable acrosswide ranges of populations and clinical environments.

Methods: :
We have developed the Berkeley Rudimentary Vision Tests(BRVT),for testing visual acuity, systematically simplifying the acuitytasks (LogMAR charts, Single tumbling E’s, and gratings)and testing distances (4m, 1m and 25cm) to measure acuitiesto LogMAR = 2.9 (20/16000, 6/4800). For visual field testing,we have developed a hand held perimeter for measuring peripheralfields, and novel computerized and tangent screen methods forassessing central fields. We have also experimented with usinga standard tangent screen using test distances of 250 cm and50 cm to test central and peripheral fields respectively

Results: :
Applying these procedures to test subjects with severe visualimpairment, we find acuity can be measure with good reliability(test-retest discrepancy SD = 0. 12 for newly trained testers).Single Tumbling E acuity can easily be measured up to LogMAR= 2.0 which gives zero as the Functional Acuity Score. Pooreracuities (LogMAR = 2.6 for E’s, 2.9 for gratings) canalso be measured reliably. Field measurements are slower andmore problematic. Size and location of binocular field defectsdepend on the angle of convergence, so that the short viewingdistances used in all bowl and arc perimeters may give resultsthat are not representative of peripheral defects at longerviewing distances. Tangent screens do not allow testing beyond55 degrees (50 cm test distance). We obtain reasonably goodtest/retest reliability for the 50 points (SD = +/-7) obtainedfor the central fields, but we consider it is impractical tomeasure peripheral fields under both monocular and binocularviewing conditions.

Conclusions: :
It should be recognized that visual acuities poorer than LogMAR= 2.0 are easily measurable, so that FAS = 0 is not the lowerlimit of acuity. Mainly for practical reasons, we recommenddiscarding binocular testing of visual fields, and using a 3:1weighting for the better eye to calculate the Functional FieldScore.